Electroluminescent organic semiconductors, also called OLEDs, are currently used mainly for flat-screen displays. However, they are becoming increasingly important in normal light applications, since they have high luminosity and low current consumption. In general, an electroluminescent organic semiconductor consists of a substrate on which a light-emitting organic material is arranged between two electrodes. The electrodes, very often made of a metal or a metal oxide such as indium-doped tin oxide (ITO) or indium-doped zinc oxide (IZO), serve to distribute the charge carriers, which generate light upon recombination, as uniformly as possible over the surface of the organic material. A better luminous efficacy is achieved through the large-area distribution. Thereby, electrons are initiated into the organic material by the cathode, while the anode provides the required positive charge carriers in the form of holes.
The organic material typically consists of several sequences of layers which have different tasks. FIG. 10 shows a typical structure of two electrodes, 200 and 300, and the “OLED stack” arranged between them, from H. Becker, et al., SID Digest (2005). The electrons or holes are transported to the layer intended for photon generation through the individual layer sequences, the thicknesses of which are given as examples in FIG. 10. In this case, these are the three uppermost layers of the stack, which comprises at least one organic layer 1. At the same time, the lower layer sequences serve to limit exciton diffusion or block undesired hole or electron transport. For example, layers S-TAD and 1-TNATA serve as hole transporters or electron blockers. Through this, holes or electrons are kept in the layer intended for recombination, so that the recombination efficiency and thus the luminous efficacy increase. Basically speaking, the light generated by the charge carrier recombination can be extracted through the cathode or the anode, or even through both.